So I had a hard drive (SSD) failure some time ago (it lasted 5 years of intense use, so I kinda expected that to happen). Luckily I had my Time Capsule running all the time, so it was a no brainer to buy a new SSD for my Macbook Air and restore it.
However after restore I found out that my laptop wasn't quite as fast as it used to be, moreover I'd get frequent freezes & beach-balling that would last up to 20 seconds. Needless to say, I was quite concerned - I was running many system diagnostics, tried cleaning it up, did SMC & PRAM reset, but nothing seemed to help much.
What was the issue?